Ceramic multilayer substrate and method for manufacturing the same

ABSTRACT

Disclosed are a ceramic multilayer substrate formed by vertically stacking and firing a plurality of ceramic substrates, in which a connection bar is longitudinally formed on connection areas between internal patterns and an external terminal of each ceramic substrate, thereby preventing metallic conductive layers of the internal patterns from being deformed during processing the external terminal and stably connecting the internal patterns to the external terminal, and a method for manufacturing the substrate. The ceramic multilayer substrate comprises pattern layers formed on surfaces of parts or all of the ceramic substrates so as to form designated circuit elements; connection bars longitudinally formed in the ceramic substrates within a part of the pattern layers extended to the edges of the ceramic substrates so as to exchange signals with the outside; at least one through hole being formed on the edges of the stacked ceramic substrates so as to be opened to the outside and exposing the connection bar; and an external terminal formed on an inner wall of the through hole.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a ceramic multilayer substratewith an improved connection structure between internal patterns and anexternal terminal, and a method for manufacturing the substrate, andmore particularly to a low temperature co-fired ceramic multilayersubstrate formed by vertically stacking and firing a plurality ofceramic substrates, in which a connection bar is longitudinally formedon connection areas between internal patterns and an external terminalof each ceramic substrate, thereby preventing metallic conductive layersof the internal patterns from being deformed during processing theexternal terminal and stably connecting the internal patterns to theexternal terminal, and a method for manufacturing the substrate.

[0003] 2. Description of the Related Art

[0004] A technique for manufacturing a low temperature co-fired ceramic(hereinafter, being referred to as “LTCC”) substrate is a process inwhich an internal electrode and passive elements (R, L, and C) for givencircuits are formed a green sheet made of glass ceramic by a screenprinting method using a metal with high electric conductivity such asAg, Cu, or etc., and a plurality of the green sheets are stackedvertically and then fired (generally at less than 1,000° C.) so as tomanufacture MCM (multi-chip modules) and multi-chip packages.

[0005] Since the ceramic substrate and the metallic elements areco-fired, the LTCC technique can form the passive elements (R, L, and C)within a module, thereby obtaining a complex configuration includingmany components and being advantageous in terms of miniaturization.

[0006] Since the LTCC substrate comprises the embedded passive elements,the LTCC substrate can be formed as a SOP (System-On-Package), therebyminimizing a parasitic effect generated in parts of a SMD (SurfaceMounted Device). Further, the LTCC substrate reduces electrical noisegenerated at soldering parts in surface mounting, thereby improvingelectrical characteristics of the manufactured device, and reduces thenumber of solderings, thereby improving the reliability of themanufactured device. Moreover, the LTCC substrate minimizes atemperature coefficient of resonant frequency (T_(f)) by adjusting athermal expansion coefficient, thereby controlling characteristics of adielectric resonator.

[0007] The LTCC multilayer substrate is formed by forming circuits in asingle ceramic substrate and vertically stacking a plurality of theceramic substrates. Therefore, external terminals to be connected to theoutside must be formed on an outer surface of the LTCC substrate andelectrically connected to circuit patterns within the substrate.

[0008]FIGS. 1 and 2 show “a stack electronic component”, in which alaminated substrate having internal circuits is provided, via holes arelongitudinally formed through the substrate, and external electrodes areformed by filling the via holes with a conductor, as disclosed byJapanese Patent Laid-open Publication No. Hei8-37251. As shown in FIGS.1 and 2, via holes 7 are formed through a stack structure 5 and filledwith conductors 9, and the conductors 9 within the via holes 7 areconnected to the internal circuits. Then, through holes 10 are formedthrough the stack structure 5 and the conductors 9 are exposed to thethrough holes 10. The exposed conductors 9 serve as external electrodes4 for electronic components. In this Japanese Publication, since theconductors 9 formed in the via holes 7 become the external electrodes 4,the external electrodes 4 have uniform dimensions and shapes and areeasily formed.

[0009] However, the above Japanese Publication has a problem as follows.The rectangular via holes 7 are simultaneously formed longitudinallythrough plural stacked green sheets by a punching method or etc. In thiscase, as shown in FIG. 3, the stacked green sheets are compressed in adirection of the punching by shear stress, and the internal metalpatterns on the green sheets are not exposed at the via holes 7. Theinternal patterns must be exposed at the via holes 7 so as to beconnected to the conductors 9 formed in the via holes 7 for serving asthe external electrodes. However, the Japanese Publication as shown inFIGS. 1 and 2 does not solve the above-described problem.

[0010] There are various methods for forming external electrodes in theconventional low temperature co-fired ceramic multilayer substrate.First, as shown in FIG. 4, an internal pattern 2 a is extended to an endof each ceramic substrate and exposed to the outside. Then, the ceramicmultilayer substrate 3 is formed by stacking and firing the pluralceramic substrates at a high temperature, and an external electrode 4 ais formed on an side surface of the ceramic multilayer substrate 3 bydeposition without forming any through hole on the ceramic multilayersubstrate 3 by the punching method. This method assures a connectionbetween the internal patterns and the external electrode. However, afterthe ceramic multilayer structure is cut into a plurality of unit ceramicmultilayer substrates 3, the surface of the ceramic multilayer substrate3 must be ground so as to expose the internal patterns 2 a prior toforming the external electrode 4 a. Therefore, this method complicates amanufacturing process of the substrate and does not satisfy arequirement for mass production.

[0011] Further, FIG. 5 illustrates a further method for forming externalelectrodes. Herein, a through hole being quarter-circular in shape isformed on a corner of each ceramic substrate so as to expose an internalpattern 2 b, and an external electrode 4 b is formed in each throughhole. Then, the ceramic multilayer substrate 3 is formed by stacking aplurality of the ceramic substrates, thereby integrating the externalelectrodes 4 b into one external terminal. In this case, since theexternal electrodes 4 b must be respectively formed on the ceramicsubstrates, the manufacturing process is very complicated. Further,since the dimensions of all the substrates are not uniform due to adifference of contraction ratios between individual substrates, theceramic multilayer substrate is easily damaged by an external impact, oretc.

[0012] Moreover, FIG. 6 illustrates another method for forming externalelectrodes. Herein, a through hole being quarter-circular in shape isformed on a corner of each substrate so as to expose an internal pattern2 c. Then, the ceramic multilayer substrate 3 is formed by stacking aplurality of the ceramic substrates, and external electrodes 4 c aresimultaneously formed in the plural through holes by the deposition.This method is generally used in forming external electrodes on aconventional low temperature co-fired ceramic multilayer substrate. Asshown in FIG. 6, since the through holes of the ceramic multilayersubstrate 3 are not precisely aligned with each other, a material forforming the external electrodes is not uniformly deposited in everythrough hole and the connection between the internal patterns and theexternal electrode becomes poor.

[0013]FIG. 7 illustrates yet another method for forming externalelectrodes, being similar to the method disclosed by Japanese PatentLaid-open Publication No. Hei8-37251. First, a plurality of ceramicgreen sheets are stacked vertically so as to form the ceramic multilayersubstrate 3. Then, a through hole is formed on a corner of the ceramicmultilayer substrate 3 and an external electrode 4 d is formed in thethrough hole by the deposition. In this case, as described in FIG. 3,internal patterns 2 d are not exposed at the through hole in a step forforming the through hole, thereby causing the same problem of not beingconnected to the external electrode 4 d.

[0014] Therefore, there is required in the art a method forsimultaneously forming through holes on every sheet of a ceramicmultilayer substrate by a punching method so as to simplify amanufacturing process of the ceramic multilayer substrate and improvethe connection between the internal patterns and the external electrode.

SUMMARY OF THE INVENTION

[0015] Therefore, the present invention has been made in view of theabove problems, and it is an object of the present invention to providea ceramic multilayer substrate for maintaining a connection betweeninternal patterns and an external electrode even in case a plurality ofceramic green sheets provided with internal patterns are stackedvertically and a through hole is formed at an area for the externalterminal of the ceramic multilayer substrate, and a method formanufacturing the substrate.

[0016] It is another object of the present invention to provide to aceramic multilayer substrate in which a plurality of ceramic greensheets are stacked vertically and a through hole is formed on theceramic multilayer substrate so as to form an external terminal therein,thereby simplifying a manufacturing process of the multilayer substrateand improving quality of the multilayer substrate, and method formanufacturing the substrate.

[0017] In accordance with one aspect of the present invention, the aboveand other objects can be accomplished by the provision of a ceramicmultilayer substrate formed by stacking and firing a plurality ofceramic substrates, comprising: pattern layers formed on surfaces ofparts or all of the ceramic substrates so as to form designated circuitelements; connection bars longitudinally formed in the ceramicsubstrates within a part of the pattern layers extended to the edges ofthe ceramic substrates adjacent to the edges so as to exchange signalswith the outside; at least one through hole being formed on the edges ofthe stacked ceramic substrates so as to be opened to the outside andexposing the connection bar; and at least one an external terminalformed on the inner walls of the said through holes.

[0018] In accordance with a further aspect of the present invention,there is provided a method for manufacturing a multilayer substrate bystacking and firing a plurality of ceramic substrates, comprising thesteps of: preparing a plurality of ceramic substrates, each of theceramic substrates having a designated thickness; forming pattern layerson surfaces of ceramic substrates so as to form circuit elements;forming via holes longitudinally in the ceramic substrates within a partof the pattern layers extended to edges of the ceramic substratesadjacent to the edges so as to exchange signals with the outside;forming connection bars by filling the via holes with a material beingelectrically connected to the pattern layers; stacking a plurality ofthe ceramic substrates; forming at least one through hole longitudinallyon the edges of the stacked ceramic substrates so as to expose theconnection bars to the outside; and forming at least one externalterminal in said through hole by deposition.

[0019] In accordance with another aspect of the present invention, thereis provided a method for manufacturing a multilayer substrate bystacking and firing a plurality of ceramic substrates, comprising thesteps of: preparing a plurality of ceramic substrates, each of theceramic substrates having a designated thickness; forming via holeslongitudinally in the ceramic substrates adjacent to edges of theceramic substrates; forming connection bars by filling the via holeswith a conductive material; forming pattern layers on surfaces ofceramic substrates so as to form circuit elements such that theconnection bars are located within a part of the pattern layers extendedto the edges of the ceramic substrates so as to exchange signals withthe outside; stacking a plurality of the ceramic substrates; forming atleast one through hole longitudinally on the edges of the stackedceramic substrates so as to expose the connection bars to the outside;and forming at least one external terminal in said through hole bydeposition.

[0020] In accordance with still another aspect of the present invention,there is provided a method for manufacturing multilayer substrates bystacking and firing a plurality of ceramic substrates, comprising thesteps of: preparing a plurality of ceramic substrate sheets, each beingprovided with scribe lines so as to be cut into a plurality of ceramicsubstrates and having a designated thickness; forming a plurality ofsame pattern layers on surfaces of ceramic substrate sheets so as toform circuit elements; forming via holes longitudinally in the ceramicsubstrate sheets within a part of the pattern layers extended to thescribe lines of the ceramic substrate sheets adjacent to the scribelines so as to exchange signals with the outside; forming connectionbars by filling the via holes with a material being electricallyconnected to the pattern layers; stacking a plurality of the ceramicsubstrate sheets; forming through holes longitudinally on the scribelines of the stacked ceramic substrates so as to expose the connectionbars to the outside; forming external terminals in the through holes bydeposition; and cutting the stacked ceramic substrate sheets along thescribe lines into a plurality of ceramic multilayer substrates.

[0021] In accordance with yet another aspect of the present invention,there is provided a method for manufacturing multilayer substrates bystacking and firing a plurality of ceramic substrates, comprising thesteps of: preparing a plurality of ceramic substrate sheets, each beingprovided with scribe lines so as to be cut into a plurality of ceramicsubstrates and having a designated thickness; forming via holeslongitudinally in the ceramic substrate sheets adjacent to the scribelines; forming connection bars by filling the via holes with conductivematerial; forming a plurality of same pattern layers on surfaces ofceramic substrate sheets so as to form circuit elements such that theconnection bars are located within a part of the pattern layers extendedto the scribe lines of the ceramic substrates so as to exchange signalswith the outside; stacking a plurality of the ceramic substrate sheets;forming through holes longitudinally on the scribe lines of the stackedceramic substrates so as to expose the connection bars to the outside;forming external terminals in the through holes by deposition; andcutting the stacked ceramic substrate sheets along the scribe lines intoa plurality of ceramic multilayer substrates.

[0022] A stack structure in accordance with the present invention isformed by stacking a plurality of layers, thereby producing a package.The layers are properly selected from materials having electric,dielectric, and magnetic characteristics. Particularly, the layer uses aceramic green sheet with a designated thickness. A pattern layer isformed in a designated shape on the green sheets by depositing a metalthereon, and serves as circuit elements when the green sheets arestacked. The pattern layers are made of metal such as Ag, Cu, or etc.The plural ceramic sheets are stacked and fired at a low temperature,thereby being formed as a stack structure referred to as a “lowtemperature co-fired ceramic multilayer substrate”.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

[0024]FIG. 1 is a perspective view of a conventional multilayersubstrate after the cutting so that external terminals are exposed tothe outside;

[0025]FIG. 2 is a perspective view of the conventional multilayersubstrate of FIG. 1 prior to the cutting so that the external terminalsare exposed to the outside;

[0026]FIG. 3 is a schematic view illustrating problems generated informing the multilayer substrate of FIG. 1;

[0027]FIG. 4 is a perspective view of showing a multilayer substratecomprising an external terminal formed by a conventional method;

[0028]FIG. 5 is a perspective view showing a multilayer substratecomprising an external terminal formed by a further conventional method;

[0029]FIG. 6 is a perspective view showing a multilayer substratecomprising an external terminal formed by another conventional method;

[0030]FIG. 7 is a perspective view showing a multilayer substratecomprising an external terminal formed by yet another conventionalmethod;

[0031]FIG. 8 is a cross-sectional view of a multilayer substrate inaccordance with the present invention;

[0032]FIG. 9 is a plan view of one ceramic substrate of the multilayersubstrate in accordance with the present invention;

[0033]FIG. 10 is a perspective view of the multilayer substrate of FIG.8;

[0034]FIG. 11 is a cross-sectional view of the multilayer substrate inaccordance with the present invention;

[0035]FIGS. 12A to 12G show a method for manufacturing a ceramicmultilayer substrate in accordance with a first embodiment of thepresent invention;

[0036]FIGS. 13A to 13G show a method for manufacturing a ceramicmultilayer substrate in accordance with a second embodiment of thepresent invention;

[0037]FIGS. 14A to 14H show a method for manufacturing a ceramicmultilayer substrate in accordance with a third embodiment of thepresent invention; and

[0038]FIGS. 15A to 15H show a method for manufacturing a ceramicmultilayer substrate in accordance with a fourth embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Now, preferred embodiments of the present invention will bedescribed in detail with reference to the annexed drawings. FIG. 8 is across-sectional view of a multilayer substrate in accordance with thepresent invention, and FIG. 9 is a plan view of one ceramic substrate ofthe multilayer substrate in accordance with the present invention. FIG.10 is a perspective view of the multilayer substrate of FIG. 8.

[0040] As shown in FIGS. 8 and 9, a pattern layer 102 in a designatedpattern is formed on each of ceramic substrates 103. An end of thepattern layer 102 is extended to an edge of the ceramic substrate 103 soas to exchange signals with the outside. It is unnecessary to form thissignal exchangeable pattern on all the ceramic substrates 103. That is,the signal exchangeable pattern may not formed on parts of the ceramicsubstrates 103.

[0041] The present invention employs the ceramic substrate 103 providedwith a through hole 105 being semicircular in shape. The through hole105 provides a space for forming an external electrode 104 therein.Further, in case a stack structure is formed by stacking a plurality ofthe ceramic substrates 103 made from a ceramic substrate sheet, thethrough holes 105 are formed through the stack structure before thestack structure is cut into a plurality of ceramic multilayer substratesso that the external electrode is simply formed. The through hole 105being circular in shape is formed across two neighboring substrates 103,and then is changed into a semicircular shape so as to be opened to theoutside by cutting the stack structure into the plural multilayersubstrate.

[0042] A connection bar 110 is formed in the ceramic substrate 103 byfilling a via hole located between the pattern layer 102 and the throughhole 105. One side of the connection bar 110 contacts the through hole105 so as to be exposed at an inner surface of the through hole 105, andthe other side of the connection bar 110 contacts the pattern layer 102.Differently from the pattern layer 102, the connection bar 110 islongitudinally formed through the ceramic substrate 103 and directlycontacts the external electrode 104. The external electrode 104 isformed on the inner wall of the through hole 105, and connected to thepattern layer 102 and the connection bar 110, thereby serving toexchange external signals with the internal patterns.

[0043]FIG. 10 shows the multilayer substrate using the connection bars110 of the present invention, in which the external electrode 104 isconnected to both the internal pattern layers 102 and the connectionbars 110.

[0044] The pattern layer 102 is made of a metallic deposition film, andthe connection bar 110 is formed by filling the via hole (not shown)with a metallic conductor so as to be electrically connected to thepattern layer 102. Preferably, the connection bar 110 is cylindrical inshape. However, the connection bar 110 may be formed in various shapesso as to be exposed at the wall surface of the through hole 105.

[0045] Preferably, the outer circumference of the through hole 105passes through the center of the connection bar 110, and a diameter ofthe connection bar 110 is smaller than a width of the pattern layer 102.Since the connection bar 110 is longitudinally formed through thesubstrate 103, the via hole having a large diameter reduces a strengthof the substrate 103 and increases an amount of the metallic conductorfilling the via hole, thereby increasing the production cost and causinga difficulty in easily and swiftly producing the substrate 103. In orderto solve above problems, it is preferable to form the via hole within anarea of the pattern layer 102.

[0046] As described above, in case the external electrode 104 iselectrically connected to the pattern layer 102 by the connection bar110, a degree of the electrical connection between the externalelectrode 104 and the internal pattern layer 102 is improved.Conventionally, since the pattern layer is formed only on the uppersurface of the substrate, the connection between the external terminaland the internal patterns is achieved by a line contact. On the otherhand, in the present invention comprising the connection bars, since acontact area between the internal patterns and the external terminal isincreased and the connection between the connection bar and the externalterminal is obtained by an area contact, the degree of the connectionbetween the internal patterns and the external terminal is improved.

[0047] Further, compared to the conventional case, the formation of theconnection bar improves a process for manufacturing the multilayersubstrate. Hereinafter, along with the description of the improvedeffect of the process, a method for manufacturing a multilayer substrateby stacking a plurality of ceramic substrates in accordance with a firstembodiment of the present invention will be described in detail withreference to FIGS. 12A to 12G.

[0048] A) A ceramic substrate 203 with a designated thickness isprepared.

[0049] B) A pattern layer 202 for forming circuit elements is formed onthe ceramic substrate 203. The plural pattern layers 202 of thevertically stacked ceramic substrates 203 form various circuit elements.The pattern layer 202 is made of a metal deposition film.

[0050] C) Via holes 211 are formed within an end of the pattern layer202 extended to an edge of the ceramic substrate 203 so as to exchangesignals with the outside. The via hole 211 is longitudinally formed onthe ceramic substrate 203 adjacent to the edge of the ceramic substrate203. Preferably, a diameter of the via hole 211 is a little smaller thana width of the pattern layer 202. The via hole 211 is formed in only apart of the pattern layer 202 extended to the edge of the ceramicsubstrate 203 so as to exchange signals with the outside, and other viaholes (not shown) are formed so as to exchange signals with otherinternal patterns of the ceramic substrate 203. Since the via holes 211are formed simultaneously with other via holes for connecting thepatterns formed on the upper and lower surface of the ceramic substrate203 to each other, the via hole 211 is simply formed without increasingthe number of manufacturing steps. Preferably, the via hole 211 has thesame diameter as those of the via holes for connecting the patternsformed on the upper and lower surfaces of the ceramic substrate 203 toeach other.

[0051] D) The via hole 211 is filled with a material for beingelectrically connected to the exposed pattern layer 202, thereby beingformed as a connection bar 210. The connection bar 210 is made of ametallic conductor so as to be electrically connected to the patternlayer 202.

[0052] E) A plurality of the ceramic substrates 203 formed by theaforementioned steps are stacked vertically. Parts or all of the stackedceramic substrates 203 comprise the connection bar 210 formed by fillingthe via hole 211, and the connection bar 210 is connected to theinternal patterns of the corresponding ceramic substrate 203.

[0053] F) A through hole 205 is longitudinally formed on the edge of thestacked ceramic substrates 203 so as to expose the pattern layers 202and the connection bars 210. The through hole 205 is semicircular inshape so as to be opened to the outside, and passes through theconnection bars 210. That is, the connection bars 210 are exposed at theinner wall of the through hole 205. Preferably, the outer circumferenceof the through hole 205 passes through the center of the connection bar210.

[0054] G) An external terminal 204 is formed on an inner circumferenceof the through hole 205. The external terminal 204 is formed bydepositing a metal on the inner circumference of the through hole 205,and is connected to the pattern layers 202 and the connection bars 210.

[0055] Since the through hole is formed through the stack structureformed by stacking the plural ceramic substrates, the above-describedmanufacturing method in accordance with the first embodiment uniformlyforms the external electrode. Further, since the metallic connection baris formed on the pattern layer connected to the outside, the connectionbar is still exposed to the outside by shear stress generated in thepunching process, thereby preventing a poor connection between theinternal patterns and the external electrode due to the deformation ofthe ceramic substrate. Moreover, a large connection area between theinternal patterns and the external electrode improves a degree of theconnection therebetween.

[0056] The method for manufacturing a multilayer substrate of thepresent invention may be modified as follows. That is, in accordancewith a second embodiment of the present invention, a step for forming avia hole is performed prior to a step for forming a pattern layer. FIGS.13A to 13G illustrate a method for manufacturing a multilayer substratein accordance with the second embodiment of the present invention.

[0057] A) A ceramic substrate 303 with a designated thickness isprepared.

[0058] B) Identically with the step C of the first embodiment, via holes311 are formed in the ceramic substrate 303. A position of the via hole311 is designated so that the via hole 311 is located within a patternlayer formed later, and the number of the via holes 311 is properlypredetermined so that the via holes 311 is located within the patternlayer for exchanging signals with the outside.

[0059] C) The via holes 311 are filled with a metallic conductor,thereby being formed as connection bars 310. The same as the firstembodiment, the connection bar 310 is longitudinally formed in theceramic substrate 303.

[0060] D) A pattern layer 302 is formed on the ceramic substrate 303 sothat the connection bars 310 are located within an area of the patternlayer 302.

[0061] E) to G) Identically with the first embodiment, a plurality ofthe ceramic substrates 303 formed by the aforementioned steps arestacked vertically, a through hole 305 is longitudinally formed on theedge of the stacked ceramic substrates 303, and an external terminal 304is formed on an inner circumference of the through hole 305.

[0062] The present invention further provides a method for manufacturinga multilayer substrate in which a multilayer substrate sheet ismanufactured and then cut into plural multilayer substrates, therebyperforming a mass production of multilayer substrate products. Thismethod is achieved by a third embodiment of the present invention andhereinafter, will be described in detail with reference to FIGS. 14A to14H.

[0063] A) A ceramic substrate sheet 403 with a designated thickness isprepared. The ceramic substrate sheet 403 is provided with scribe lines408 so as to be cut into a plurality of ceramic substrates.

[0064] B) A plurality of same pattern layers 402 for forming circuitelements are formed on the ceramic substrate sheet 403. The pluralpattern layers 402 of the vertically stacked ceramic substrate sheets403 form various circuit elements. The pattern layers 402 are made of ametal deposition film.

[0065] C) Via holes 411 are formed within the pattern layers 402extended to the scribe lines 408 of the ceramic substrate sheet 403 soas to exchange signals with the outside. The via holes 211 arelongitudinally formed on the ceramic substrate sheet 403 adjacent to thescribe lines 408 of the ceramic substrate sheet 403. Preferably, adiameter of the via hole 411 is a little smaller than a width of thepattern layer 402. The via hole 411 is formed in only a part of thepattern layer 402 extended to the scribe lines 408 of the ceramicsubstrate sheet 403 so as to exchange signals with the outside, andother via holes (not shown) are formed so as to exchange signals withother internal patterns of the ceramic substrate sheet 403. Since thevia holes 411 are formed simultaneously with other via holes forconnecting the patterns formed on the upper and lower surface of theceramic substrate sheet 403 to each other, the vie hole 411 is simplyformed without increasing the number of manufacturing steps. Preferably,the via hole 411 has the same diameter as those of the via holes forconnecting the upper and lower patterns.

[0066] D) The via holes 411 are filled with a material for beingelectrically connected to the exposed pattern layers 402, thereby beingformed as connection bars 410. The connection bars 410 are made of ametallic conductor so as to be electrically connected to the patternlayers 402.

[0067] E) A plurality of the ceramic substrate sheets 403 formed by theaforementioned steps are stacked vertically. Parts or all of the stackedceramic substrate sheets 403 comprise the connection bar 410 formed byfilling the via hole 411, and the connection bar 410 is connected to theinternal patterns of the corresponding ceramic substrate sheet 403.

[0068] F) Through holes 405 are longitudinally formed on the scribelines 408 of the stacked ceramic substrate sheets 403 so as to exposethe pattern layers 402 and the connection bars 410. The through hole 405is cylindrical in shape, and passes through the connection bars 410.That is, the connection bars 410 are exposed at the inner wall of thethrough hole 405. Preferably, the outer circumference of the throughhole 405 passes through the center of the connection bar 410.

[0069] G) External terminals 404 are formed on inner circumferences ofthe through holes 405. The external terminals 404 are formed bydepositing a metal on the inner circumferences of the through holes 405,and are connected to the pattern layers 402 and the connection bars 410.

[0070] H) The stacked ceramic substrate sheets 403 are cut along thescribe lines 408 into a plurality of ceramic multilayer substrates 400,each having a desired size.

[0071] Similarly with the first embodiment, since a through hole isformed on the stack structure formed by stacking a plurality of thesubstrates, this manufacturing method in accordance with the thirdembodiment uniformly forms the external electrode. Further, since themetallic connection bar is formed on the pattern layer connected to theoutside, the connection bar is still exposed to the outside by shearstress generated in the punching process, thereby preventing a poorconnection between the internal patterns and the external electrode dueto the deformation of the ceramic substrate. Moreover, a largeconnection area between the internal patterns and the external electrodeimproves a degree of the connection therebetween. In addition, themanufacturing method of the third embodiment applies the steps forforming the connection bars and the through holes to a mass productionof the multilayer substrates, thereby performing a mass production of alow temperature co-fired ceramic multilayer substrate products havingthe aforementioned effects.

[0072] The method for manufacturing a multilayer substrate of the thirdembodiment may be modified as follows. That is, in accordance with afourth embodiment of the present invention, a step for forming via holesis performed prior to a step for forming pattern layers. FIGS. 15A to13H illustrate a method for manufacturing a multilayer substrate inaccordance with the fourth embodiment of the present invention.Similarly with the second embodiment, in the manufacturing method of thefourth embodiment, connection bars are first formed, and then patternlayers are formed.

[0073] A) Identically with the third embodiment, a ceramic substratesheet 503 with a designated thickness is prepared and provided withscribe lines 508 so as to be cut into a plurality of ceramic substrates.

[0074] B) Identically with the step C of the third embodiment, via holes511 are formed in the ceramic substrate sheet 503. Positions of the viaholes 511 are designated so that the via holes 511 are located withinpattern layers formed later, and the number of the via holes 511 isproperly predetermined so that the via holes 511 are located within thepattern layers for exchanging signals with the outside.

[0075] C) The via holes 511 are filled with a metallic conductor,thereby being formed as connection bars 510. The same as the thirdembodiment, the connection bars 510 are longitudinally formed in theceramic substrate sheet 503.

[0076] D) Pattern layers 502 are formed on the ceramic substrate sheet503 so that the connection bars 510 are located within areas of thepattern layers 502.

[0077] E) to G) Identically with the third embodiment, a plurality ofthe ceramic substrate sheets 503 formed by the aforementioned steps arestacked vertically, through holes 505 are longitudinally formed on thescribe lines 508 of the stacked ceramic substrate sheets 503, andexternal terminals 504 are formed on inner circumferences of the throughholes 505.

[0078] In accordance with the above-described embodiments of the presentinvention, multilayer substrates for stably maintaining the connectionbetween the internal patterns and the external electrodes aremanufactured. Conventionally, a process for forming a through hole afterthe stacking of the ceramic substrates was not used due to theaforementioned problems. However, as shown in FIG. 11, in accordancewith a method for manufacturing multilayer substrates of the presentinvention, the connection bar 110 formed within the internal patternlayer 102 is still exposed at the wall of the through hole, therebybeing connected to the external electrode 104 formed in the throughhole. Further, the internal pattern layer 102 is connected to theconnection bar 110, thereby being stably connected electrically to theexternal electrode 104.

[0079] As apparent from the above description, since a through hole isformed on the stack structure formed by stacking a plurality of thesubstrates provided with pattern layers, the external electrode isuniformly formed on the ceramic multilayer substrate. Further, since ametallic connection bar is formed on the pattern layer connected to theoutside, the connection bar is still exposed to the outside by means ofshear stress generated in a step for punching the through hole, therebypreventing a poor connection between the internal patterns and theexternal electrode due to the deformation of the ceramic substrate.Moreover, a large connection area between the internal patterns and theexternal electrode improves a degree of the connection therebetween.

[0080] In addition, a method for manufacturing multilayer substrates ofthe present invention applies steps for forming the connection bars andthe through holes to a mass production of the multilayer substrates,thereby performing a mass production of a low temperature co-firedceramic multilayer substrate products having the aforementioned effects.

[0081] A low temperature co-fired ceramic multilayer substrate inaccordance with the present invention connects the internal patternlayers to the external electrode via the connection bar formed on eachceramic substrate, thereby improving the degree of the electricalconnection between the internal pattern layers and the externalelectrode. Conventionally, since the pattern layer is formed only on theupper surface of the substrate, the connection between the externalterminal and the internal patterns is achieved by a line contact. On theother hand, in the present invention comprising the connection bars,since a contact area between the internal patterns and the externalterminal is increased and the connection between the connection bar andthe external terminal is obtained by an area contact, the degree of theconnection between the internal patterns and the external terminal isimproved.

[0082] Although the preferred embodiments of the present invention havebeen disclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A ceramic multilayer substrate formed by stackingand firing a plurality of ceramic substrates, comprising: pattern layersformed on surfaces of parts or all of the ceramic substrates so as toform designated circuit elements; connection bars longitudinally formedin the ceramic substrates within a part of the pattern layers extendedto the edges of the ceramic substrates adjacent to the edges so as toexchange signals with the outside; at least one through hole beingformed on the edges of the stacked ceramic substrates so as to be openedto the outside and exposing the connection bar; and at least oneexternal terminal formed on the inner walls of the said through holes.2. The ceramic multilayer substrate as set forth in claim 1, wherein thepattern layers are made of a metal deposition film, and the connectionbars are formed by filling via holes formed in the ceramic substrateswith a metallic conductor so as to be electrically connected to thepattern layers.
 3. The ceramic multilayer substrate as set forth inclaim 1, wherein a circumference of the through hole passes through thecenter of the connection bar.
 4. The ceramic multilayer substrate as setforth in claim 1, wherein a diameter of the connection bar is not largerthan a width of the pattern layer extended to the edge of the ceramicsubstrate so as to exchange signals with the outside.
 5. A method formanufacturing a multilayer substrate by stacking and firing a pluralityof ceramic substrates, comprising the steps of: preparing a plurality ofceramic substrates, each of the ceramic substrates having a designatedthickness; forming pattern layers on surfaces of ceramic substrates soas to form circuit elements; forming via holes longitudinally in theceramic substrates within a part of the pattern layers extended to edgesof the ceramic substrates adjacent to the edges so as to exchangesignals with the outside; forming connection bars by filling the viaholes with a material being electrically connected to the patternlayers; stacking a plurality of the ceramic substrates; forming at leastone through hole longitudinally on the edges of the stacked ceramicsubstrates so as to expose the connection bars to the outside; andforming at least one external terminal in the said through hole bydeposition.
 6. A method for manufacturing a multilayer substrate bystacking and firing a plurality of ceramic substrates, comprising thesteps of: preparing a plurality of ceramic substrates, each of theceramic substrates having a designated thickness; forming via holeslongitudinally in the ceramic substrates adjacent to edges of theceramic substrates; forming connection bars by filling the via holeswith a conductive material; forming pattern layers on surfaces ofceramic substrates so as to form circuit elements such that theconnection bars are located within a part of the pattern layers extendedto the edges of the ceramic substrates so as to exchange signals withthe outside; stacking a plurality of the ceramic substrates; forming atleast one through hole longitudinally on the edges of the stackedceramic substrates so as to expose the connection bars to the outside;and forming at least one external terminal in the said through hole bydeposition.
 7. The method for manufacturing a multilayer substrate asset forth in claims 5 or 6, wherein the pattern layers are made of ametal deposition film, and the connection bars are formed by filling thevia holes with a metallic conductor so as to be electrically connectedto the pattern layers.
 8. The method for manufacturing a multilayersubstrate as set forth in claims 5 or 6, wherein the connection bars arecylindrical in shape, and a circumference of the through hole passesthrough the center of the connection bar.
 9. The method formanufacturing a multilayer substrate as set forth in claims 5 or 6,wherein a diameter of the connection bar is not larger than a width ofthe pattern layer extended to the edge of the ceramic substrate so as toexchange signals with the outside.
 10. A method for manufacturingmultilayer substrates by stacking and firing a plurality of ceramicsubstrates, comprising the steps of: preparing a plurality of ceramicsubstrate sheets, each being provided with scribe lines so as to be cutinto a plurality of ceramic substrates and having a designatedthickness; forming a plurality of same pattern layers on surfaces ofceramic substrate sheets so as to form circuit elements; forming viaholes longitudinally in the ceramic substrate sheets within a part ofthe pattern layers extended to the scribe lines of the ceramic substratesheets adjacent to the scribe lines so as to exchange signals with theoutside; forming connection bars by filling the via holes with amaterial being electrically connected to the pattern layers; stacking aplurality of the ceramic substrate sheets; forming through holeslongitudinally on the scribe lines of the stacked ceramic substrates soas to expose the connection bars to the outside; forming externalterminals in the through holes by deposition; and cutting the stackedceramic substrate sheets along the scribe lines into a plurality ofceramic multilayer substrates.
 11. A method for manufacturing multilayersubstrates by stacking and firing a plurality of ceramic substrates,comprising the steps of: preparing a plurality of ceramic substratesheets, each being provided with scribe lines so as to be cut into aplurality of ceramic substrates and having a designated thickness;forming via holes longitudinally in the ceramic substrate sheetsadjacent to the scribe lines; forming connection bars by filling the viaholes with conductive material; forming a plurality of same patternlayers on surfaces of ceramic substrate sheets so as to form circuitelements such that the connection bars are located within a part of thepattern layers extended to the scribe lines of the ceramic substrates soas to exchange signals with the outside; stacking a plurality of theceramic substrate sheets; forming through holes longitudinally on thescribe lines of the stacked ceramic substrates so as to expose theconnection bars to the outside; forming external terminals in thethrough holes by deposition; and cutting the stacked ceramic substratesheets along the scribe lines into a plurality of ceramic multilayersubstrates.
 12. The method for manufacturing multilayer substrates asset forth in claims 10 or 11, wherein the pattern layers are made of ametal deposition film, and the connection bars are formed by filling thevia holes with a metallic conductor so as to be electrically connectedto the pattern layers.
 13. The method for manufacturing multilayersubstrates as set forth in claims 10 or 11, wherein the connection barsare cylindrical in shape, and a circumference of the through hole passesthrough the center of the connection bar.
 14. The method formanufacturing multilayer substrate as set forth in claims 10 or 11,wherein a diameter of the connection bar is not larger than a width ofthe pattern layer extended to the edge of the ceramic substrate so as toexchange signals with the outside.